PHOTOSPHERIA OF NYCTIPHANES KORVEGICA. 341 



EXPLANATION OF PLATE XXIII, 



Illustrating Messrs. Vallentin's and Cunningham's Memoir on 

 "The Photospheria of Nyctiphanes Norvegica, G. O. 

 Sars." 



List of Reference Letters. 



ct. Cuticle, co. Cornea, ep. Epidermis. /. r. Fibrous ring. /. m. Fibril- 

 lar mass. ga. Pair of ventral ganglia. /. Lens. lac. Blood lacuna, p. c. 

 Posterior cellular layer, re. Reflector. 



Fig. 1. — Section of the photospherion of the first abdominal somite in situ. 

 The plane of the section is perpendicular to the principal axis of the animal's 

 body, and passes through the principal axis of the organ. 



Fig. 2. — Excernal surface of the posterior thoracic photospherion, seen after 

 slight compression in the fresh condition. (Zeiss A, oc. 2.) 



Fig. 3. — Section of the photospherion of the ocular peduncle. The plane of 

 the section passes through the principal axis of the organ. 



Fig. 4. — Section of the photospherion of the ocular peduncle perpendicular 

 to the principal axis of the organ. 



Fig. 5. — Section of anterior thoracic photospherion from a young individual 

 a quarter of an inch long. 



Fig. 6. — Similar section of the organ of the first abdominal somite at the 

 same stage. 



Fig. 7. — Fresh preparation of a photospherion carefully crushed beneath the 

 cover-glass. Transmitted light. (Zeiss C C, oc. 2.) 



